<?php
    //生成验证码
    session_start();
    //session_register('CheckCode');
    //PHP4.2以上版本不需要用session_register()注册SESSION变量
    $type='gif';
    $width= 55;
    $height= 30;
    header("Content-type: image/".$type);
    srand((double)microtime()*1000000);
    if(isset($_GET['action']))
    {
        $randval=randStr(4,$_GET['action']);
    }
    else
    {
        $randval=randStr(4,'');
    }
    if($type!='gif'&&function_exists('imagecreatetruecolor'))
    {
        $im=@imagecreatetruecolor($width,$height);
    }else
    {
        $im=@imagecreate($width,$height);
    }
    $r=Array(225,211,255,223);
    $g=Array(225,236,237,215);
    $b=Array(225,236,166,125);
    $key=rand(0,3);
    $backColor=ImageColorAllocate($im,$r[$key],$g[$key],$b[$key]);//背景色（随机）
    $borderColor=ImageColorAllocate($im,127,157,185);//边框色
    $pointColor=ImageColorAllocate($im,255,170,255);//点颜色
    @imagefilledrectangle($im,0,0,$width - 1,$height - 1,$backColor);//背景位置
    @imagerectangle($im,0,0,$width-1,$height-1,$borderColor); //边框位置
    $stringColor=ImageColorAllocate($im,255,51,153);
    for($i=0;$i<=100;$i++){
        $pointX=rand(2,$width-2);
        $pointY=rand(2,$height-2);
        @imagesetpixel($im,$pointX,$pointY,$pointColor);
    }
    @imagestring($im,5,5,1,$randval,$stringColor);
    $ImageFun='Image'.$type;
    $ImageFun($im);
    @imagedestroy($im);
    $_SESSION['CheckCode']=$randval;
    function randStr($len=6,$format='ALL'){
        switch($format){
            case 'ALL'://生成包含数字和字母的验证码
                $chars='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'; break;
            case 'CHAR'://仅生成包含字母的验证码
                $chars='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'; break;
            case 'NUMBER'://仅生成包含数字的验证码
                $chars='0123456789'; break;
            default :
                $chars='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'; break;
        }
        $string='';
        while(strlen($string)<$len)
            $string.=substr($chars,(mt_rand()%strlen($chars)),1);
        return $string;
    }
?>